U.S. Pat. No. 3,787,230 discloses a method of coating an article by applying an aqueous slurry of a powder paint onto the surface. The powder paint is a commercial powder, having an average particle size of 36 micrometers, and the slurry has to be kept homogeneous by agitation during preparation and use. On storage the solid matter of such a slurry will settle, and it is technically unattractive to redisperse it again immediately before use.
U.S. Pat. No. 4,100,315 discloses a method of preparing aqueous coating powder dispersions containing as the binder a solid epoxy resin, which is micronized in water in the presence of a specific combination of surfactants. For many applications, however, the presence of surfactants in the cured coating is not desirable.
Patent application Ser. No. 382,534, filed May 27, 1982, now U.S. Pat. No. 4,446,257, issued May 1, 1984, discloses the preparation of an aqueous coating powder suspension in which the powder particles comprise an intimate mixture of binder components:
(a) an epoxy resin/amine adduct having terminal amino groups; PA0 (b) a crosslinking component, and optionally PA0 (c) a solid polyepoxide, PA0 (a) dispersing pigment powder having a particle size less than 20 micrometers in a liquid, solvent-free epoxy resin, PA0 (b) dispersing the resultant paste in water, PA0 (c) reacting the resultant dispersion with a secondary amine, and, optionally, a primary amine, the amount of amine or amines being sufficient to provide at least one N--H function per epoxy group of the epoxy resin, at a temperature in the range 40.degree. C. to 100.degree. C., and PA0 (d) neutralizing the resulting suspension of epoxy-amine adduct coated particles, and PA0 (e) optionally, adjusting the concentration of the resulting dispersion within the range 35 to 75%w solids by addition of water. PA0 (f) adding to an aqueous binder composition prepared by the process of the invention, a crosslinking agent, and PA0 (g) adjusting, if necessary, the concentration of the composition by addition of water to ensure a solids content in the range 10 to 65%w.
the mixture having a softening point of at least 70.degree. C., wherein the solid paint components are intimately blended, extruded and ground to a powder, and the particle size in the suspension is reduced below 20 micrometers by milling.